On Saturday, hundreds of thousands of people around the world are expected to take part in a global day of action under the World Social Forum's (WSF) banner, "another world is possible."

Ever since 2001, the WSF has taken place parallel - and in opposition - to the World Economic Forum in Davos, Switzerland, which describes itself as "striving towards a world-class corporate governance system." The WSF has become one of the most important places for discussion and debate for the movement for a different kind of globalisation. This year, however, the mega-event will be replaced by an attempt to re-root the counter-globalisation movement through a series of locally organised, globally coordinated protests and discussions.

The WSF was born of a "cycle of struggles" against a particular form of capitalist globalisation. Its beginnings are generally traced back to either the Zapatista rebellion against the neoliberal North American free trade agreement in Mexico in 1994, or the spectacular protests that shut down the World Trade Organisation (WTO) Ministerial in Seattle in 1999.

For many on the left, the arrival of this diverse "movement of movements" signalled a new sense of possibility for change. Only a few years earlier, Margaret Thatcher had been able to argue, with some conviction, that to neoliberal globalisation, "there is no alternative."

Today, however, the world looks very different. Ever since (and of course including) Seattle, almost every round of WTO negotiations has collapsed. The Free Trade Area of the Americas agreement has faced a similar fate. In Europe, the neoliberal EU constitution was rejected by referendums in France and the Netherlands. And across Latin America and beyond, a series of electoral victories have been won on an anti-neoliberal ticket.

This turn of events has been due in no small part to the struggles and arguments forwarded by the movement born in Chiapas and Seattle. And yet, ironically, it is these and other victories which today present it with its greatest challenges.

The movement has generally defined itself negatively, in terms of what it is against. In itself, this is not a problem. In fact, it has been one of its greatest strengths: allowing it to recognise what it has in common - a shared opposition to neoliberalism - despite its internal heterogeneity. If from the beginning, the focus had been on formulating more precisely what it was fighting for, it would likely have long collapsed under the weight of sectarian, ideological debate.

However, with the hegemony of neoliberalism now on the wane, the challenge - and opportunity - with which the movement is presented is to redefine what it is opposed to. Of course, one option would be to maintain the focus on neoliberalism, the most fundamentalist form of free market ideology. Hegemonic it may no longer be, but the doctrine is certainly not dead.

Alternatively, it could choose to locate itself more explicitly in the longer, broader, tradition of anti-capitalism. Obviously, this too would involve active opposition to the neoliberal project. But it would also call for a deeper negation of the present, exposing - and developing forms of political organisation capable of taking on - the capitalist organisation of society more generally.

While the first option certainly would seem to offer the greatest opportunities for building broad coalitions in the short term, it brings with it certain dangers. Not least of all, it obscures the fact that a capitalist market society - including in its more regulated, Keynesian forms (which some within the counter-globalisation movement are already proposing as an alternative to neoliberalism) - always involves violence and exploitation. It is premised upon denying the majority of humanity the right to life, unless it sells its time, energy and creativity on the market. It involves enclosing and defending the very social wealth this humanity produces and is then denied access to.

For the movement to continue claiming: "another world is possible," it needs to be clearer about what it is that characterises this one. Importantly, though, these debates need to remain rooted within a political practice. As soon as they become issues of ideology or political position, rather than questions connected to the realities of everyday lives and struggles, they will stagnate and lose meaning. It is the opportunity to conduct these discussions of global relevance on a local level that gives this weekend's global day of action its importance.